This application is based on and claims priority from Japanese Patent Application Nos. Hei. 2-335940, Hei. 2-335941 and Hei. 2-335942 filed Nov. 30, 1990, respectively, the disclosures of which are incorporated herein by reference.
The present invention relates to an ocular lens system for viewfinders of cameras.
Such a type of ocular lens is disclosed in, for example, Japanese Patent Unexamined Publication No. Hei 1-142521. The lens disclosed in this publication relates to a single positive meniscus lens whose concave surface is directed to the pupil. A distance (backfocus) from a screen (focal plane) to the ocular lens is set at a long distance relative to the focal length in order to meet the requirement of viewfinders for single lens reflex (SLR) cameras and the like (in particular, for finder system having penta-mirror).
However, such a lens suffers from a disadvantage that a difference in diopter between a central portion and a marginal portion of a view field, corresponding to a curvature of field of the focusing lens system, and astigmatism would be increased. Also, since the aspherical effect is small, a height of an off-axis marginal ray is increased, so that it is impossible to make the finder system small in size. Furthermore, a thickness of the finder system is large, it would be difficult to use an inexpensive plastic for the material of the lens. Thus, the cost for the lens would be increased.